SQL 2008 HierarchyID - Select X descendants down

How can I query a table which has a column of data type HIERARCHYID and get a list of descendants X levels deep under an employee?

Here is the current structure:

CREATE TABLE [dbo].[Employees]开发者_StackOverflow中文版(
    [NodeId] [hierarchyid] NOT NULL,
    [EmployeeId] [int] IDENTITY(1,1) NOT NULL,
    [FirstName] [varchar](120) NULL,
    [MiddleInitial] [varchar](1) NULL,
    [LastName] [varchar](120) NULL,
    [DepartmentId] [int] NULL,
    [Title] [varchar](120) NULL,
    [PhoneNumber] [varchar](20) NULL,
    [IM] [varchar](120) NULL,
    [Photo] [varbinary](max) NULL,
    [Bio] [varchar](400) NULL,
    [Active] [bit] NULL,
    [ManagerId] [int] NULL
)

I wanted to add a little to the above. In addition to selecting a branch of a tree, you often want descendants of only a certain depth. To accomplish this, many tables using add an additional computed column for "depth" ( something like [Depth] AS (myHierarchy.GetLevel]() ). With this extra column you can run queries like the following to limit by depth.

SELECT @MaxDepth       = 3,

SELECT @theParent      = Hierarchy,
       @theParentDepth = Depth
FROM   myTreeTable T 
WHERE  T.RowID         = @RowID

SELECT    myHierarchy
FROM      myTreeTable T
WHERE     T.myHierarchy.IsDescendantOf(@theParent) = 1  AND
          T.Depth < (@theParentDepth  + @MaxDepth)

Note, you may want to index the computed column (probably combined with or including some other columns) if you are relying on it heavily.